In this section we consider the scalaron decay into massless scalars minimally coupled to gravity.
The scalaron decay width into two massless (or very low mass) scalar bosons was calculated in
Refs. [1]}, [2]}, [3]}. Here we follow our paper [3]}, where
another approach was used based on papers [5]}, [6]}, which allows to derive closed
equation in the case of
an arbitrary time evolution of the source field (in our case the scalaron, \(R(t)\) ), while the traditional
methods are valid only for the harmonic oscillations of the source.
